1. Field of the Invention
This invention relates to fluid pressure operated actuators for producing rotational motion for such purposes as rotary valve operation for example.
2. Description of the Prior Art
Fluid pressure operated actuators for producing rotational motion are generally well known in the prior art wherein it is customary to mechanically interconnect a plurality of pressure operated cylinder-mounted pistons with a rotatable output shaft such as illustrated in U.S. Pat. Nos. 3,153,317 to Manor et al and 3,099,287 to Manor. In the systems disclosed in these patents, the mechanical interconnection between the pistons and output shaft takes the form of a flexible band or rigid shaft wherein bi-directional linear movement of the pistons causes bi-directional rotation of the output shaft. While useful for the purposes disclosed, these systems tend to be physically bulky and require complicated fluid control circuits. More particularly, the mechanical linkage systems disclosed in the noted patents to manor and Manor et al require the cylinder-mounted pistons to travel a distance equal to the circumferential distance traveled by the rotatable output shaft due to the direct mechanical linkage therebetween.
Some flexibility has been achieved in the prior art by use of chain linkage systems providing double runs for each pressure operated piston, such as disclosed in U.S. Pat. No. 2,449,269 to Austin, FIG. 3. The system disclosed in the Austin patent converts the linear displacement of the cylinder pistons into linear displacement of an output member but does not disclose a system wherein the required length of the operating cylinders may be decreased while maintaining the same capability for rotational displacement of an output shaft having a fixed axis of rotation. The piston arrangement and fluid valving system of Austin is also incapable of producing reversible rotary motion such as contemplated by the present invention.
Another disadvantage of the fluid control systems for actuators of the type disclosed in the patents to Manor and Manor et al. has been the use of complicated reversing valves which are designed to supply and exhaust fluid pressure to and from every cylinder in the system through passages provided in the reversing valve itself. It is known in certain types of spool valve operating systems, such as disclosed in U.S. Pat. No. 3,596,560 to Butterworth for example, to supply constant pressure to one face of a double acting piston (valve spool) while selectively pressurizing the exhausting fluid pressure to an opposing face of the piston which is of larger effective cross-sectional area. However, no arrangement such as disclosed in the Butterworth patent has been employed in a pressure operated actuator having a pair of pressure operated, cylinder-mounted pistons mechanically linked with an output shaft adapted to rotate about a fixed axis.